The following prior art appears relevant:
U.S. patentsPat. No.Kind CodeIssue DatePatentee4,365,4741982 Dec. 28Stig G. Carlqvist4,526,0081985 Jul. 2Carol O. Taylor, Sr6,483,207B12002 Nov. 19Robert W. Redlich7,134,279B22006 Nov. 14Maurice A. White et al.7,171,811B12007 Feb. 6David M. Berchowitz et al.